Project Summary What does it mean to know something about the world? Central to any theory of knowledge is a theory of concepts, those mental representations that allow us to categorize information in the world. In this project, we attempt to understand concepts by studying their neural instantiation. The central aim of this project is to advance our understanding of the neural representation of concepts via a characterization of similarity. The broader goal of this research program is to develop a strategy for understanding the neural representation of all types of knowledge; however, to make this problem more tractable, we are focusing on a specific type of concept - concrete objects - and on a particular type of knowledge about those concepts - their visual appearance. Specifically, (1) We aim to describe the neural representation of object concepts by characterizing neural tuning to features in a multidimensional similarity space; (2) We aim to examine variation in the neural representations of object concepts, across concepts, across individuals, and across attentional states; (3) We aim to explore to role of sleep-dependent consolidation processes in the acquisition of new object concept knowledge; (4) We aim to develop innovative methods for the characterization of neural similarity more generally.